Maybe you’ve seen a little story today about mercury, pregnancy, fish, and attention-deficit/hyperactivity disorder (ADHD). If you haven’t, you probably will. The news release headline says, “Prenatal mercury exposure may be associated with risk of ADHD-related behaviors.” The modifiers in there “may be” and “related” won’t stop the mental math from this study translating as “pregnant+mercury=ADHD,” and it won’t stop headlines from implying as much. Mix in a confusing finding about eating fish during pregnancy–protective or harmful?–and what’s a science consumer to do?

The study relied on a cohort of children born from 1993 to 1998 and their mothers. About 10 days after each mother gave birth, she filled out a questionnaire about what she’d eaten during pregnancy–including fish broken down by category–and gave up a hair sample. Investigators at Brigham and Women’s Hospital in Boston evaluated the hair for levels of methylmercury, an organic form of mercury that the central nervous system readily takes up. When the children reached the age of 8, they underwent testing that evaluated behaviors related to ADHD. The study was originally designed to assess the relationship, if any, between exposure to polychlorinated biphenyls contaminating a local harbor and neurodevelopment.

According to the findings, ADHD-related behaviors in the 607 evaluated 8-year-olds increased with increasing methylmercury values from mom’s hair around the time she gave birth. These associations were stronger for boys than girls for some features, with a slightly increased risk for ADHD-related behaviors above a mercury value of 1 microgram/gram in the hair. But fish consumption during pregnancy was linked to reduced levels of ADHD-related behaviors in the children.

Pregnancy and fish

What’s a pregnant woman to do, given that a lot of fish we’d like to eat contain a lot of mercury? “Fish is the predominant source of mercury intake for pregnant women,” says Bruce Lanphear, who wrote a commentary accompanying the study, both published in Archives of Pediatrics and Adolescent Medicine. That information, he adds, “shouldn’t change the recommendations to pregnant women about eating fish that is low in mercury.” Which fish are which? Here’s a handy guide, but briefly, salmon, trout, and catfish tend to be low mercury while shark, tuna, and mackerel (sob!) are no-nos.

So, first take-home is, you can keep eating fish. Just don’t eat fish that have a lot of mercury in them. Nothing’s changed there. In fact, eating fish without a lot of mercury seems to be protective, so get thee to a good fish market and pick something tasty, low-mercury, and sustainable for dinner. What we need here is a sustainable × low-mercury guide to make all of this easier.

ADHD and mercury

But what about this ADHD and mercury link? Well, this study doesn’t actually report a link between mercury and ADHD. As study senior author Susan Korrick, assistant professor of medicine at Brigham and Women’s Hospital in Boston, notes, “it’s really important to keep in mind that we did not look clinically at children diagnosed with ADHD.” This cohort was just a general population of children tracked after being born healthy and vaginally, and as with any children, no one knew when they were born how they’d turn out. So some might have ADHD, but overall, they simply represent a general population. “We were looking at behaviors largely across the normal range, which is very different from looking at a clinical diagnosis of ADHD,” Korrick says. “It’s beyond the scope of this research to make inferences about clinical ADHD.” ADHD has a large inherited component [PDF], so if your child has ADHD, you don’t need to waste hours guiltily assessing your fish intake during pregnancy.

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The Minnesota Department of Health must have not gotten the 1999 memo. “…the Public Health Service, the American Academy of Pediatrics and vaccine manufacturers agree that thimerosal-containing vaccines should be removed as soon as possible.” http://www.fda.gov/ohrms/dockets/dockets/04p0349/04p-0349-ref0001-05-Tab-03-Joint-Statement-Thimerosal-AAP-PHS-vol6.pdf

Look at the LBRB commenter’s reference at table 2 and notice the mean of exposure for “controls” is close to the mean of exposure for the rest of the exposed group. It does not provide a clue as to exposure thresholds that indicate damage compared to zero exposure. This is not science.

Look at what happens to silicon wafers (used to make PC processors) with one part per million mercury contamination. “Transition metals, in particular, must be kept below parts per billion concentrations for electronic applications.” http://en.wikipedia.org/wiki/Wafer_(electronics)

The concentration of mercury in a Thimerosal preserved flu shot is 50 parts per million. This is 250 times the threshold for D009 mercury hazardous waste. It is illegal to flush it or toss it in the trash.

“The morality that pollution is criminal only after legal conviction is the morality that causes pollution.”

W. Eugene and Aileen Smith, Minamata: The Story of the Poisoning of a City, and of the People Who Chose to Carry the Burden of Courage, 1975.

“Look at what happens to silicon wafers (used to make PC processors) with one part per million mercury contamination. “Transition metals, in particular, must be kept below parts per billion concentrations for electronic applications.” http://en.wikipedia.org/wiki/Wafer_(electronics)”

This has zero relevance to the discussion. The human brain is not a wafer of single crystal silicon. Iron is a transition metal. It will cause major problems if it contaminates silicon. It is vital the keeping humans alive.

Anon: “Thank you for your reply. The organic mercury leaves quicker but the inorganic stays longer. So the Dose-Time Product is greater. That is concern here.”

If this is your concern, you will be relieved to read the actual paper rather than internet discussions.

From the study: “A much lower brain concentration of total Hg was observed in the thimerosal monkeys compared with the MeHg monkeys, that is, a 3- to 4-fold difference for an equivalent exposure of Hg”

Again, I’ll note that none of this has anything to do with the article above.

“You failed to mention that the amount of Hg++ in the brain was almost 5 times higher from the thimerosal group than the methylmecury group. Hg++ is what causes brain injury.”

How do you get 5 times higher from “Absolute inorganic Hg concentrations in the brains of the thimerosal-exposed monkeys were approximately twice that of the MeHg monkeys”.

OK, 2 not five. Still, something to consider. Did you?

Are you surprised that if ethyl mercury is broken down quicker than methyl, the amount of inorganic mercury would be higher if measured before it is all broken down?

To be a bit more precise–They measured mercury levels at 28days after last exposure. Consider this sentence from the abstract:

“The initial and terminal half-life of Hg in blood after thimerosal exposure was 2.1 and 8.6 days, respectively, which are significantly shorter than the elimination half-life of Hg after MeHg exposure at 21.5 days.”

So, at 28 days they are have gone through 3 half lives for thimerosal. But barely over 1 half life of methyl mercury. One expects that more will have been converted from thimerosal.

Long term, there will be more inorganic mercury in the brain from methyl mercury.

And, I note, you are the one now arguing that there is a “safe” mercury. Only inorganic (Hg++) causes damage? Based on what data?

I think I’ll stick to what the paper says rather than what you claim it says.

(1) The request to read Evidence of Harm is to the author of this blog.

(2) Yes the hungry lie is that there is no evidence of harm. Stop feeding it.

(3) Denial that there are thresholds of damage to central processors (with billions of transistors on one die) is an example of the denial that the thresholds of damage to developing brains from mercury is not known.

(4) Total Hg was lower but the inorganic mercury was higher with ethylmercury from Thimerosal exposure. So the the dose-time product is higher.